Summary

Creates a group capture

Prototype

lpeg.Cg (patt [, name])

Description

It groups all values returned by patt into a single capture. The group may be anonymous (if no name is given) or named with the given name.

An anonymous group serves to join values from several captures into a single capture. A named group has a different behavior. In most situations, a named group returns no values at all. Its values are only relevant for a following back capture or when used inside a table capture.

This example parses a list of name-value pairs and returns a table with those pairs:

lpeg.locale(lpeg)

local space = lpeg.space^0
local name = lpeg.C(lpeg.alpha^1) * space
local sep = lpeg.S(",;") * space
local pair = lpeg.Cg(name * "=" * space * name) * sep^-1
local list = lpeg.Cf(lpeg.Ct("") * pair^0, rawset)
t = list:match("a=b, c = hi; next = pi") --> { a = "b", c = "hi", next = "pi" }

Each pair has the format name = name followed by an optional separator (a comma or a semicolon). The pair pattern encloses the pair in a group pattern, so that the names become the values of a single capture. The list pattern then folds these captures. It starts with an empty table, created by a table capture matching an empty string; then for each capture (a pair of names) it applies rawset over the accumulator (the table) and the capture values (the pair of names). rawset returns the table itself, so the accumulator is always the table.

See Also ...

Lua functions

lpeg.B - Matches patt n characters behind the current position, consuming no input
lpeg.C - Creates a simple capture
lpeg.Carg - Creates an argument capture
lpeg.Cb - Creates a back capture
lpeg.Cc - Creates a constant capture
lpeg.Cf - Creates a fold capture
lpeg.Cmt - Creates a match-time capture
lpeg.Cp - Creates a position capture
lpeg.Cs - Creates a substitution capture
lpeg.Ct - Creates a table capture
lpeg.locale - Returns a table of patterns matching the current locale
lpeg.match - Matches a pattern against a string
lpeg.P - Converts a value into a pattern
lpeg.print - Outputs debugging information to stdout
lpeg.R - Returns a pattern that matches a range of characters
lpeg.S - Returns a pattern that matches a set of characters
lpeg.setmaxstack - Sets the maximum size for the backtrack stack
lpeg.type - Tests if a value is a pattern
lpeg.V - Creates a non-terminal variable for a grammar
lpeg.version - Returns the LPeg version

Topics

Lua bc (big number) functions
Lua bit manipulation functions
Lua LPEG library
Lua package functions
Lua PCRE regular expression functions
Lua script extensions
Lua string functions
Lua syntax
Lua table functions
Lua utilities
Regular Expressions
Scripting
Scripting callbacks - plugins

(Help topic: lua=lpeg.Cg)